The present invention relates to filters and more particularly to belt filters of the type adapted to filter liquids such as cutting and coolant liquids used in the machining of manufactured parts.
Filters have long been used for such applications in which a flexible strip of sheet material comprising the filter media is caused to be advanced through the interior space of a filter tank, which filter tank receives the unfiltered liquid.
The filter belt passes along the bottom of the tank and in the lower region thereof a perforated or otherwise open partition is overlapped by a section of the filter belt. Upon development of a suction pressure in a collection chamber beneath the open partition, filtering flow of the liquid will occur through the filter belt, into the collection chamber and thence to return to the system.
Continuous loops of chain are typically mounted along either side of the tank lying atop the filter belt side edges extending through the tank interior space. Typically, chain flights extend across the width of the belt to enable carrying off of the filter cake or sludge accumulating atop the filter belt as the filtration process proceeds.
This arrangement is used in relatively large sized tanks and depends on the chains being disposed along either edge of the filter belt in order to weigh down the edges of the filter belt and create a sealing engagement with the tank bottom to prevent bypass flow of the dirty liquid past the filter belt.
U.S. Pat. No. 3,091,336 to Hirs is typical of such filters.
This arrangement is highly successful, but involves relatively elaborate structure including power driven chains and relatively complex drive systems are necessitated.
In some instances, a permanent type belt filter is utilized, a relatively costly construction which requires backwashings, scraping, precoating, etc., greatly increasing the complexity of the apparatus.
In U.S. Pat. No. 4,159,948 there is disclosed a similar filter arrangement in which a disposable filter media is moved through the tank in similar fashion without the use of a permanent conveyor belt or chains. In order to seal the edges of the filter belt, a liquid seal is employed at the side and back edges of the length of filter material disposed in the tank. This liquid seal is achieved by use of a clean liquid receiving reservoir located at the rear side of the tank and maintained at a higher liquid level to provide an inflow of clean liquid along the periphery of the tank. This requires a diversion of flow from the system, which may substantially impair the capacity of the system. This also requires an auxiliary tank, complicating the tank structure.